Electricity: measuring and testing – Magnetic – Calibration
Reexamination Certificate
1999-06-10
2001-06-26
Strecker, Gerard R. (Department: 2862)
Electricity: measuring and testing
Magnetic
Calibration
C324S232000, C324S242000
Reexamination Certificate
active
06252393
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to sensor arrays and more particularly to normalizing and calibrating a sensor array.
An array of sensors can be used to detect and/or measure the dimension of defects in metal components and parts. In this regard, each sensor in the array is capable of producing an electrical signal indicative of a defect in a metal component or part. Multiple sensors can be used together as an array to scan an area of the component or part that is larger than if a single sensor was used. However, in order to accurately detect and/or measure the defect, it is important that all of the sensors in the array react in the same way (i.e., produce the same electrical signal) to the same defect. For this to occur, the sensors in the array should all have the same dynamic range and respond identically in signal amplitude to the same defect.
To obtain uniform reaction from sensors, the sensors are normalized and calibrated. For example, flexible eddy current array sensors used to inspect aircraft engine components have been previously normalized and calibrated using two separate specimens, one to normalize the signal from all sensor elements and the other to calibrate the element signal level. For normalization, all elements are scanned across a linear feature. A correction factor and offset is calculated for each element from its signal level and saved for use during later testing of a part. For calibration, one of the sensor elements is used to scan a single notch on a test specimen in two dimensions. This process can be time consuming because a significant amount of time is required to properly align the sensor array to each test specimen. In this regard, the sensor needs to be aligned with the test specimen at minimum two times. Furthermore, the two-dimensional scan is done at a high spatial resolution. Moreover, the result's accuracy is limited because the data are obtained using a test specimen that may not match the geometric shape of the part to be inspected so the part test conditions may not match the calibration conditions. Thus, the data may not sufficiently represent the scanning conditions of a sensor array used to scan components or parts having complex surfaces.
SUMMARY OF THE INVENTION
Thus, there is a need for a faster, simpler, and more accurate system and method to normalize and calibrate sensor arrays. The present invention is a system, test specimen and method for normalizing and calibrating an array of sensors using one or more scans of a single test specimen. Notably, only one alignment of the sensor to the test specimen is required. The test specimen is preferably made of the same or similar type of material and is of a similar geometric shape (e.g., a simple flat surface or a more complex surface) as the metal component or part to be scanned for defects. The test specimen further comprises at least one linear feature and multiple notches that are machined into the surface of the test specimen. Both the linear feature and the notches cause the sensors in the array to produce electrical signals that are used to normalize and calibrate the sensor arrays. The method uses the electrical signal trace produced by each sensor in the array and caused by the respective sensor detecting the linear feature on the test specimen during scanning to remove any bias and to normalize the dynamic range of each sensor in the array. The method further uses the electrical signal trace produced by particular sensors in the array and caused by the respective sensor detecting one or more of the multiple notches of the test specimen during scanning to establish the gain settings for and calibrate each sensor in the sensor array.
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Breedlove Jill M.
General Electric Company
Goldman David C.
Strecker Gerard R.
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